RADIO ASTRONOMY AND SETI
“Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is.”
-
Douglas Adams, the Hitchhiker’s
Guide to the Galaxy
Astronomy,
arguably the oldest of the physical sciences, is mankind’s eternal struggle to
understand and demystify the phenomena occurring in the vast, huge,
mind-boggling enormity of space. In the past century, we have come a long way
from the painstakingly catalogued astronomical records of Tycho Brahe - the
1930’s and 40’s saw the invention of radio telescopes, which ushered in a
revolution in astronomy. Nowadays, as ever, every advancement in space
research, every new phenomenon discovered, raises again that most befuddling of
questions: Are we truly alone in the cosmos?
Anyone who has
read Carl Sagan’s ‘Cosmos’ should be familiar with the concept of radio
astronomy. It is a subfield of astronomy that studies celestial objects at
radio frequencies of the electromagnetic spectrum. One might ask – why radio,
in particular? One reason is astronomical: many phenomena in the universe show
up best in one part of the spectrum, and analysing radio signals allows us to
“see” some of the most extreme, energetic (and often bizarre) processes in
space – things that cannot be detected by optical (“conventional”) astronomy.
Another reason is practical: our atmosphere is transparent to visible light
(wavelengths 300 – 700 nm) and also to radio waves with wavelengths between
about 1 mm and 30 m. Optical and radio signals from outer space are the
portions of the electromagnetic spectrum we can detect most clearly.
The detection
and study of any celestial source of radio waves is possible with radio
astronomy, including but not limited to: Jupiter, stars (including the Sun),
pulsars, active galactic nuclei, and supernova remnants. Even the Cosmic
Microwave Background, the almost uniform microwave radiation that permeates the
entire universe and is the remnant of the Big Bang, was first discovered in the
same way. Radio astronomical measurements also allow us to study fundamental
forces like gravity and magnetism, and model the formation of galaxies. With
the advent of radio astronomy, it’s as if we’ve suddenly opened up our senses
to hitherto undetected signals coming in from all over the cosmos, and
discovered a whole new universe (not literally, of course).
Another way to
practise radio astronomy is to shoot radar beams and bounce them off a
celestial object (for example, Mercury), and study the signal received. This is
in fact the technique used by the world’s largest single-dish telescope located
in Arecibo, Puerto Rico, and has been likened to shining a torch onto heavenly
bodies in order to see them better, which is as amazing as it sounds . . .
All radio
telescopes have two basic components – a large radio antenna and a radiometer
or radio receiver. The telescope’s sensitivity essentially depends on the area
(effective aperture) of the antenna and the sensitivity of the radiometer.
While designs vary widely, the most familiar type is the radio reflector
consisting of a parabolic antenna. Great efforts are taken to protect and
shield radio telescopes from man-made radio signals to avoid interference,
often by placing them in valleys, shielded by mountains on all sides. Eventually,
though, it becomes impractical to keep increasing the size of the parabolic
antenna to increase sensitivity – a single dish can only be so big! Hence, the
technique of astronomical interferometry is used, in which arrays of individual
antennae are interconnected to create a massive effective aperture. This is
evident in the Very Large Array (VLA) in New Mexico, USA and in the Giant
Metrewave Radio Telescope (GMRT) near Pune, India. The largest array, LOFAR
(Low Frequency Array) is currently being constructed in Western Europe.
Individual
antennae in the Very Large Array
One of the
biggest success stories of radio astronomy is the discovery and study of
Pulsars, which are essentially extremely dense neutron stars spinning rapidly
on their axes, emitting regularly timed pulses of radio waves as they spin.
Last year I read an article in which the writer likened pulsars to “disco balls
in space”, which is possible the most brilliantly eloquent way of describing
these exotic remnants of stars. Pulsars were accidentally discovered by Jocylen
Bell and Anthony Hewish when they were searching for twinkling sources of radio
radiation. As is the case with a number of scientific breakthroughs, they
discovered anomalies in their data which later turned out to be proof of the
existence of a previously unknown celestial phenomenon!
 |
| A schematic representation of a pulsar |
Readers of Carl
Sagan’s Cosmos would also be aware of SETI (the Search for Extra-Terrestrial
Intelligence). To the layperson, SETI invokes images of the Jedi, the starship
Enterprise, or even Little Green Men. However, it is no fantasy – SETI is a
scientific search for intelligent life outside of Earth, conducted by the SETI
Institute and universities all over the world.
In 1964, Soviet
astronomer Nikolai Kardashev proposed the Kardashev Scale, a method of
measuring a civilisation’s level of technological advancement. A Type 1
civilisation utilises all the available resources of its home planet, Type 2
harnesses all the energy of its star, and Type 3 of its galaxy. So where does
mankind feature in all of this? Scientists agree that ours is a Type 0
civilisation! If the Kardashev scale is considered, there is the possibility of
numerous extraterrestrial civilisations, many of them considerably more
advanced than ours.
If so, where is
everybody? Italian physicist Enrico
Fermi suggested in the 1950s that if technologically advanced
civilizations are common in the universe, then they should be detectable in one
way or another. The Fermi paradox can be stated more completely as follows: the
size and age of the universe incline us to believe that many technologically
advanced civilizations must exist. However, this belief seems logically
inconsistent with our lack of observational evidence to support it. Either (1)
the initial assumption is incorrect and technologically advanced intelligent
life is much rarer than we believe, or (2) our current observations are
incomplete and we simply have not detected them yet, or (3) our search
methodologies are flawed and we are not searching for the correct indicators.
Radio astronomy
plays a fundamental role in SETI. As of now, our primary tool in our hunt for
extraterrestrials is the search for electromagnetic signals they might be
gregarious enough to send out into space. Gamma-Ray Bursts (GRB’s) are also
candidates for extraterrestrial communication. MIT’s John Ball suggests that an
advanced civilization that has extremely advanced technology would be
capable of transmitting GRB’s. Technosignatures, including all signs of
technology with the exception of the interstellar radio messages that define
traditional SETI, are a recent avenue in the search for extraterrestrial
intelligence. Technosignatures may originate from various sources, such
as city lights on extrasolar planets or the atmospheric contamination
created by an industrial civilization, and may be detectable in the future
with large hypertelescopes.
In any case,
SETI raises innumerable questions regarding the existence of alien life. For
example, if we were to make first contact with an alien civilisation, would
they turn out to be hostile? Or maybe the extraterrestrial races that do exist
are so technologically advanced that they choose to ignore us, just like a
human being would ignore an earthworm? Though it has a tendency to venture into
the abstract and arcane, SETI is still a fascinating field of study. In my
opinion, it would be extremely boring (and quite frankly, a let-down) if we turned
out to be the only intelligent species in the universe.
About the author
Pratik Gandhi was a delegate from India for the London International Youth Science Forum in 2013. To find out more and apply for the forum click here.
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